This is the scheme on which the circuit is based. The design is not too
big , but according to my teacher can be improved by repositioning
those 2 block mentioned above. I wish to know how is that possible ?

>>> I must decrease the size of this circuit, only by repositioning>>> the logic and the addSub modules.> The design is not too big , but according to my teacher can be> improved by repositioning those 2 block mentioned above.
Is "improved" the same as "decrease"?
It seems to mee, that you should draw a new schematic with the same
functionality, but with less ressources or less logic levels or higher
speed...

Ok, first of all I would like to apologize for the error I have made. By
"size" i meant "depth". My bad :(.
Yes in this case "improved" means "decreased" ( we're talking about the
circuit's depth ).I can't alter the code. The only way in which the
depth must be reduced is to reposition those 2 modules.